System and method for controlling concrete production

ABSTRACT

A system is designed to measure concrete rheological properties which includes a concrete plant, a measuring unit and a mix changing unit. The measuring unit includes a surface in contact with a part of a mass of the concrete mix, a shearing unit for effecting shear deformation in the mass and at least one sensor which senses a measure of the force which is transferred to the surface by the concrete mass as a result of the shear deformation. The rheological profile is produced by: a) sensing at least one measure of the force which is transferred to the surface under at least two different stress states, b) determining i) the sensitivity of each of the at least one measure to a change in stress state and ii) the workability of the mix and c) creating the rheological profile from at least the sensitivity and workability.

FIELD OF THE INVENTION

The present invention relates to concrete in general and moreparticularly to an improved system and method for the design and controlof concrete production.

BACKGROUND OF THE INVENTION

Concrete is generally prepared according to a mix design which specifiesthe proportions of the various material constituents used to produce theconcrete. For example, a concrete mix commonly described as a "1:2:4"mix refers to mix proportions of one part of cement to 2 parts of fineaggregate (such as sand) to 4 parts of coarse aggregate (such asgravel). The proportion between cement and water is also usuallyspecified. The design of the mix may depend on many factors and specificengineering requirements.

Some of these requirements relate to the rheological properties requiredfrom the mix in its fresh state during its transportation, placement andcompaction. The requirements are determined to suit specific conditionsof application, for example use of pumping in transportation, themeasure of vibration employed during compaction, the measure of cohesionand mobility needed during placing, etc.

Whilst the mechanical properties of hardened concrete are mainlyinfluenced by the water/cement ratio of the mix, the rheologicalproperties of the fresh mix are strongly influenced by the water contentand also strongly by the particle size distribution of the solidparticles in the mix and by the relative content of fine particles, inthe aggregate system.

The particle size distribution in the mix depends on the mix design aswell as on the particle size distribution within each of theconstituents from which the mix is produced. A change in the characteror size distribution of one of the aggregate constituents of a mixhaving a given design, results in changes in its rheological properties.

To offset such changes, the mix design can be modified. Suchmodifications are commonly conducted under the supervision of a concretetechnician. The suitability of the mix in its fresh state to a givenapplication requirements is commonly measured through the sheardeformation of the mix. This is commonly determined by measuring"workability" via a known test method. A common test method, known asthe "Slump Test", is especially suited for the measurement of theworkability of mixes having a soft consistency. A supporting frame inwhich a mass of concrete has been cast is lifted, allowing the concretebody to freely slump under gravity. The drop in height of the concretemass is measured.

A test method commonly used for the definition of the "workability" ofdry mixes measures the time, in seconds, it takes a body of concrete tochange its shape from a truncated cone to a cylindrical shaped bodyunder the effect of standard vibration.

Adjustments in workability are commonly achieved during production ofconcrete mixes by changing the quantity of water in the mix.

Also common in the monitoring of workability of a concrete mix whilst ina mixing drum is the measurement of the force required to mix theconcrete by rotation of the drum or the paddles in the drum. Ameasurement of the force can be obtained by monitoring the hydraulicpressure or current needed to operate the mixer motor.

The resistance to deformation of a mix can be regulated by changing theamount of water added to it. It is known how to effect an automaticadjustment to the amount of water in the mix so that a constantworkability is maintained. For example, European Patent Publication 0126 573 A1 to Durant proposed a method of controlling the quality of theconcrete mix in mobile mixers by measuring the workability of theconcrete mix and selectively adding water to achieve the requiredconsistency for the concrete mix.

Different concrete mixes can exhibit equal workabilities when measuredby different techniques and yet can possess totally differentrheological properties relating to their suitability for commonlyrequired applications. For example, when a concrete mix is designed, forpumping, its rheology is especially adjusted to be pumpable under theset of conditions.

A standard mix design "assumes" that the characteristics of the variousconstituents are constant. However, in practice, the characteristics ofa specific aggregate may vary in time. It may become necessary to changethe mix proportions in order to maintain the desired mixcharacteristics. Unfortunately, present technology does not have anyobjective procedure of accurately defining the rheological requirementsand methodically making changes to the mix proportions so as to ensurethat the final product has the required characteristics. The changes,when made, are according to a subjective and qualitative assessment of aconcrete technician. It is known to alter the amount of water within aconcrete mix in order to change the workability of the mix.

SUMMARY OF THE INVENTION

Commonly used workability tests for concrete are conventions chosen togenerate deformation in a concrete mix under set conditions for thepurpose of providing a measure of the resistance of the concrete mix todeformation. Applicant has recognized that the resistance to deformationof a concrete mix is influenced by the stress state acting on the shearplanes during the deformation. Furthermore, Applicant has realized thatdifferent mixes are differently affected in terms of their resistance todeformation following a change in the stress states acting on the shearplanes in a deformational regime.

Since, in reality, concrete is applied under various deformational modesand regimes producing different stress states, it is important toprovide a parameter which measures the change in the resistance todeformation of a given mix under changing stress states. Such aparameter reflects the internal friction of the mix governing itsbehavior between the liquid and rigid aggregate phases.

The provision of such a characteristic in the definition of the behaviorof concrete provides an important addition to the presently availabledefinition of resistance to deformation which is restricted to aparticular workability test method conducted under a given deformationalmode. A vector consisting of at least two such variables is hereinaftercalled the "Rheological Profile" of the mix. In order to obtain readingsof two such variables, at least two measurements of resistance todeformation, or related values, are conducted under at least two"measurement environments". A measurement environment is a domain withina concrete mass having a characteristic stress configuration (state andlevel) under a given condition in a deformational mode in the concretemass.

Two measurement environments could be provided, for example, by takingmeasurements under at least two deformational regimes under changingstress states. The invention offers methods by which a concrete mixundergoes shear in a sequence of at least two changing deformationalmodes during which the resistance to deformation or related values, aremeasured.

In this way, a scale is formed by which it is possible to measure anddefine variables of the rheological profile of a mix. By testing asequence of a few mixes having controlled changes in the mix design, themix required to produce any particular rheological profile isestablished.

There is therefore provided, in accordance with a preferred embodimentof the present invention, a measuring system which includes a surface, ashearing unit and at least one sensor. The surface is in contact with apart of a mass of the concrete mix. The shearing unit effects sheardeformation in the mass. The sensor senses a measure of the force whichis transferred to the surface by the concrete mass as a result of theshear deformation.

Additionally, in accordance with a preferred embodiment of the presentinvention, the surface is part of a confining envelope and the sensor ismounted on the confining envelope. There can be two sensors located ontwo different planes of the confining envelope. Alternatively, the twosensors can be located in two different measurement environments alongthe confining envelope.

Alternatively, in accordance with a further preferred embodiment of thepresent invention, the shearing unit is a rigid body and the surface isa contact surface of the rigid body in contact with the mass ofconcrete. In this embodiment, the sensor measures the resistance of theshearing unit to movement present when producing the shear deformation.Furthermore, there is a space defined between the confining envelope andthe contact surface which changes shape with the movement of the rigidbody during shear deformation. The sensor measures the change inresistance following the change in shape of the space.

Moreover, in accordance with both preferred embodiments of the presentinvention, the measuring system includes a vibrator. The two differentmeasurement environments are: operating with only the shear deformationunit and operating with both the shear deformation unit and thevibrator. The sensors can be located at two different distances from thevibrator.

Further, in accordance with a preferred embodiment of the presentinvention, the shearing unit is any one or a combination of thefollowing means: a mechanical mixer, a paddle mixer, a mechanical screw,a plunger, a hydraulic pump, a propeller and a rotatable drum. Theconfining envelope is any one or a combination of the followingcontainers: a pipe, a box, a drum and a block forming frame.

More specifically, in accordance with a still further preferredembodiment of the present invention, there is provided apparatus formeasuring the rheological profile of concrete within a container. Theapparatus includes a) a U-shaped shear box having openings at two ends,b) an upstand, c) a piston for pushing the U-shaped shear box within theconcrete towards and over the upstand, thereby to force the concrete outthe openings and either d) stress sensors placed on two non-parallelplanes for measuring the stress in the planes as a function of the shearinduced in the concrete by the shear inducing apparatus or e) movementsensors for sensing the movement of the piston. The apparatus can alsoinclude a vibrator and/or at least one acceleration sensor attached tothe shear box. The apparatus can also include connecting rods betweenthe shear box and a frame onto which are mounted stress sensors and/orpressure sensors for sensing the pressure pushing the piston.

There is also provided, in accordance with a still further preferredembodiment of the present invention, a method for generating therheological profile of a concrete mix. The steps of the method are:

a. sensing at least one measure of the force which is transferred to asurface in contact with a part of a mass of the concrete mix under atleast two different shear deformation modes;

b. from the output of step (a), determining a) the sensitivity of eachof the at least one measure to a change in deformation mode and b) theworkability of the mix; and

c. creating the rheological profile from at least the sensitivity andthe workability.

Moreover, in accordance with this preferred embodiment of the presentinvention, the shear deformation is conducted once while the mass isunder vibration and once while the mass is not under vibration. Themeasure of the force can be any of the following variables: movement,shear rate, acceleration, pressure and force.

There is additionally provided, in accordance with a still furtherpreferred embodiment of the present invention, a method for dynamicallydesigning concrete to have desired rheological properties. The methodincludes the steps of:

a. preparing a concrete mix in a concrete plant in accordance with a mixdesign indicating the proportions of solid and water components of theconcrete;

b. testing the prepared concrete mix with a concrete tester;

c. generating a rheological profile of the concrete mix from output ofthe step of testing;

d. comparing the generated rheological profile with a desiredrheological profile defining desired properties of the concrete to beproduced by the plant; and

e. adjusting the solid components of the mix design in order to produceconcrete having a rheological profile which is compatible with thedesired rheological profile.

Moreover, in accordance with this preferred embodiment of the presentinvention, the steps of preparing, testing and generating are repeatedfor at least three concrete mixes at least two of which have differentproportions of solid components and at least two of which have differentwater to solid ratios.

Still further, in accordance with this preferred embodiment of thepresent invention, the rheological profiles include a measure ofworkability and at least one of the following factors: expressions orfunctions related to the: stress state sensitivity, stress distribution,shear rate sensitivity, vibration decay, vibratability, pumpability anddeformability. The rheological properties can each have a range ofallowable values.

There is also provided, in accordance with a still further preferredembodiment of the present invention, a system which designs concrete tohave desired rheological properties. The system includes a plant, aconcrete profile measuring unit and a mix changing unit. The plantprepares a concrete mix in accordance with a mix design indicating theproportions of the solid components and water of the concrete. Theconcrete profile measuring unit, such as those described hereinabove,measures a rheological profile of the concrete produced by the plant.The mix changing unit receives the measured rheological profile and adesired rheological profile defining desired properties of the concreteproduced by the plant and indicates to the plant to adjust the solidcomponents of the concrete mix, as many times as necessary, in order toproduce concrete which has a rheological profile which is compatiblewith the desired rheological profile.

Moreover, in accordance with this preferred embodiment of the presentinvention, the mix changing unit includes a search unit which receives aquality of change criterion and determines the mix design change whichwill provide concrete having a rheological profile which is compatiblewith the desired rheological profile and which fits within the qualityof change criterion. The criterion can be a function of the cost of themix. The concrete profile measuring unit can be located within or awayfrom the plant.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further construction features of the invention will be betterappreciated in the light of the ensuing description of a preferredembodiment thereof, given by way of example only with reference to theaccompanying drawings wherein:

FIG. 1 is a block diagram illustration of a system for controllingconcrete production in accordance with a preferred embodiment of thepresent invention;

FIG. 2 is an isometric illustration of a device for testing concrete inaccordance with a preferred embodiment of the present invention;

FIG. 3 is a side view illustration of a sensing device;

FIGS. 4A and 4B illustrate the operation of the device of FIG. 2;

FIG. 4C is a graphical illustration of resistance vs. shear deformationfor two mixes deformed with the device of FIG. 2;

FIG. 5 is a flow chart illustration of the design of a nominalrheological mix;

FIG. 6 is a flow chart illustration of the use of a nominal rheologicalprofile to control a concrete mix being produced;

FIG. 7 is a block diagram illustration of an application of theinvention in a alternative, optimizing mode;

FIG. 8 is a flow chart illustration of the operation of the system ofFIG. 7;

FIG. 9A is an isometric illustration of a concrete testing device inaccordance with a second preferred embodiment of the present invention;

FIG. 9B is a sectional elevation of the concrete testing device of FIG.9A;

FIG. 9C is a graphical illustration of resistance vs. shear deformationfor two mixes deformed with the device of FIGS. 9A and 9B;

FIG. 10A is a sectional elevation of a concrete testing device inaccordance with a fourth preferred embodiment of the present invention;

FIG. 10B is a sectional elevation of a concrete testing device inaccordance with a fifth preferred embodiment of the present invention;

FIG. 11 is a sectional elevation of specially adapted pipes used with aconcrete testing device in accordance with one of the preferredembodiments of the present invention;

FIG. 12 is an isometric view of a concrete testing device in accordancewith a sixth preferred embodiment of the present invention;

FIG. 13 is a sectional detail of the concrete testing device adapted tobe inserted into a 90 degree pipe bend of a pumping system described inFIG. 12;

FIG. 14A is an illustration of the use of a concrete testing device asin FIG. 2 or FIG. 9 with a paddle mixer;

FIG. 14B is an illustration of the use of a concrete testing device inaccordance with a seventh preferred embodiment of the present invention;

FIG. 15 is an illustration of the use of the concrete testing deviceadapted for use with a mobile mixer; and

FIG. 16 is an illustration the production control of concrete blocks inaccordance with an eighth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1 which illustrates a system forcontrolling concrete production, constructed and operative in accordancewith a preferred embodiment of the present invention. The systemcomprises a concrete plant 2, a concrete tester 4 and a mix designchanger 6.

The concrete plant 2 can be any electronically controlled prior artconcrete batching plant which produces concrete from a mix designdefining the ratios of fine sand, aggregate, water and cement from whichto produce a desired concrete.

The concrete tester 4, described in more detail hereinbelow with respectto FIGS. 2, 3, 9-16, measures various properties of the concrete mixundergoing shear deformation. From these properties, a "rheologicalprofile" can be produced (either in the concrete tester 4 or in the mixdesign changer 6) which will be described in more detail hereinbelow.The rheological profile defines the rheological nature of the concretemix.

The mix design changer 6, described in more detail hereinbelow withrespect to FIGS. 5 and 6, compares the measured rheological profile witha nominal rheological profile defined as required for the concrete to beproduced. If the two match sufficiently closely, then the concrete whichhas been produced has the desired qualities. However, if the differencesbetween the two rheological profiles exceed pre-defined limits, then themix design changer 6 adjusts the percentages of fines to coarseaggregates, and/or water and cement contents, so that the concreteproduced has the desired qualities.

In another situation in which there is no definition of a requiredrheological profile and where the concrete is being processed in aconcrete processing device that induces shear deformation in theconcrete mass, the operation of the plant (as opposed to the propertiesof the mass) can be monitored in a manner discussed hereinbelow toprovide the data for the adjustments in the mix design. The resultantdesign of the concrete will be compatible with the requirements of theprocess parameters whilst also being compatible with a cost optimizationcriterion.

FIGS. 2, 3, 9-13 illustrate various measuring systems for generating thephysical measurements which are the basis of the rheological profile.FIGS. 12-16 illustrate measuring units in conjunction with concretemanufacture, production, and transportation systems. For all systems,the concrete mass is mechanically disturbed to undergo a deformationunder a given loading regime.

A First Concrete Tester

Reference is now made to FIG. 2 which illustrates a device for testingconcrete, constructed and operative in accordance with a firstembodiment of the invention.

The concrete testing device, generally designated 10, comprisesvibrating apparatus 12 and shear inducing apparatus, generallydesignated 14, for determining the rheological characteristics of theconcrete. Vibrating apparatus 12 and shear inducing apparatus 14 aremounted on to a rigid frame, generally designated 16. A plurality ofstress sensors 18 and acceleration sensors 20, of types known in theart, are attached to shear inducing apparatus 14. Other sensors, labeled31, 33 and 46 sense a measure of other steering action.

Different concrete properties can be ascertained by placing the concretetesting device inside a container 90 of concrete, and for example, bysubjecting the concrete to shear deforming and/or vibrating (as will bedescribed in detail hereinbelow), and noting the readings of sensors 18and 46. Sensors 18, 20, 31, 33 and 46 are connected, via a dataacquisition system (not shown), to a processing unit 100 for processingthe sensor data. The level of concrete for testing is indicated by line95 and generally needs to cover the top of shearing apparatus 14.

Rigid frame 16 comprises a base portion 22, a pair of vertical members24 and a top portion 26. An upstand 28 is mounted onto base portion 22between vertical members 24.

Vibrating apparatus 12 comprises an electrical or pneumatic vibrator 30,of a type known in the art, mounted onto the upper side of top portion26. Vibration induced by vibrator 30 is transferred via vertical members24 to base portion 22 and upstand 28.

Sensors 20 comprise a pair of upper and lower acceleration sensors 20aand 20b, respectively, on the shear box 34. The difference in thereadings from acceleration sensors 20a and 20b indicates the ability ofthe concrete to absorb the vibration energy, from which a vibrationdecay factor can be determined. A tension sensor 31 is fitted to one ofvertical members 24 to monitor the changing tension within the frame 16.

Shear inducing apparatus 14 includes a piston 32 and an inverted"U"-shaped shear box 34. Shear box 34 comprises two side panels 36a and36b connected to a base panel 38 such that ends 40 are open. Piston 32is fixed to top portion 26 and includes a piston rod 42 attached to basepanel 38 of shear box 34. Piston 32 is attached to a power source 44,such as a hydraulic pump with a controllable rate. A pressure sensor 46is fitted to piston 32 to measure the hydraulic pressure within piston32. An electronic ruler 33 measures the extension of piston 32.

The plurality of stress sensors 18, shown by dashed circles, areattached to the inner face of side panels 36a and 36b and base panel 38of shear apparatus 14.

Reference is now briefly made to FIG. 3 which illustrates an exemplarysensor 18. The sensor comprises a pressure sensor 21, a housing 23within which the pressure sensor 21 sits, and an elastomeric membrane 25which is in contact with the concrete mass (indicated by dots). Themembrane 25 is typically placed within the walls of the shear box 34 anddefines the surface over which the pressure is measured.

Reference is now also made to FIGS. 4A and 4B which show the operationof shear box 34. FIG. 3A shows piston rod 42 and shear box 34 in anintermediate position. FIG. 3B shows piston rod 42 extended to itsmaximum position.

Extending piston rod 42 pushes shear box 34 downwards at a controlledrate and forces the concrete sideways (shown by arrows 48) out of theopen ends 40 of shear box 34 and downwards (shown by arrows 50) overupstand 28. The width of base panel 38 is greater than the width of baseportion 22. Thus, as piston rod 42 is extended and shear box 34correspondingly descends downwards, side panels 36a and 36b close overbase portion 22 and during the latter stages of descent, concrete ispushed sideways only (as shown in FIG. 4B) out of the open ends 40. Aspiston rod 42 descends, the shape of space enclosing the concretechanges (it is reduced to the space between the shear box 34 and thebase portion 22), forcing the concrete out of shear box 34. Themultiplicity of pressure sensors 18 (not shown), some of which are inorthogonal planes, monitor the changing stresses as the concrete shearsdue to the shape change. Pressure sensor 46 and stress sensor 31 monitorthe resistance to movement of the piston rod 42.

FIG. 4C, to which reference is briefly made, illustrates exemplarychanges in resistance due to shear deformation for two types of mixes, afirst mix, labeled 0, and the first mix with more sand, labeled 1.Resistance measurements are taken as the deformation increases. Curves51 and 53 show the changing shear resistance for the 0 and 1 mixes,respectively, as the shear box 34 descends. The first datapoint, R₁ ^(i)is measured as the shear box 34 begins its descent and the seconddatapoint R₂ ^(i) is measured once the shear box 34 has come to close toits final position. Curves 51 and 53 indicate that a) the resistance isdifferent for the two types of mixes, where the resistance is less inthe first mix with less sand, and b) that the resistance changes, bydifferent amounts, as the shear deformation regime changes.

Many different measurements can be taken from the data of FIG. 4C. Forexample, the sensitivities, S⁰ and S¹, of measurements R⁰ and R¹,respectively, to deformation are defined as: ##EQU1##

Typically, measurements from all the sensors are gathered over time sothat relationships among their outputs can be established. For example,the change in output of the pressure sensor 46 and/or the stress sensor31 can be examined against readings of sensors 18 or the electric ruler33.

A third method of operation tests the concrete by measuring thedifference in behavior in shear with and without vibration. In thismethod, frame 14 is subjected to the method described above with andthen without vibration. The vibration tends to "liquefy" the concreteand reduce the effect of friction. Optionally, the intensity of thevibration can be controlled, enabling repetition of the operation undera number of vibration levels.

Curve 55 indicates the change resistance for the first mix due to thepresence of vibration and should be compared to curve 51. Curve 55 islower than curve 51, indicating that the resistance to shear deformationis lower in the presence of vibration. In addition, the change in theresistance, from R₁ ⁰ (v) to R₂ ⁰ (v), over the test is lower in thepresence of vibration. The sensitivity S⁰ (v), otherwise called the"vibratability", is defined as: ##EQU2##

Some rheological characteristics of the concrete mass, as manifestedduring the various testing operations, described hereinabove, can becalculated from the sensor data. For example, the testing machine ofFIGS. 2, 3A and 3B can produce some of the following characteristics,defined for the purpose of illustration, any collection of which form a"rheological profile":

a. Workability: A quantitative measure of the resistance to sheardeformation of a concrete mass under the influence of an external force.It can be measured with the apparatus of FIG. 2 or by other standardmeans. For instance, workability can be measured as the resistance toshear at a given rate of deformation or the time it takes to produce agiven deformation under a constant force.

b. Stress state sensitivity factor: a coefficient expressing therelationship between the resistance to shear deformation (theworkability) of a confined concrete mass and the stress state prevailingin the shear planes;

c. Stress distribution factor: a coefficient expressing the relationshipbetween the level of stresses developing on two orthogonal planes in aconcrete mass under the influence of a force vector acting normally toone of the planes;

d. Shear rate sensitivity factor: A coefficient expressing arelationship between the rate of shear induced in a concrete mass andthe resulting stresses;

e. Vibration decay factor: A coefficient expressing the rate of changein the intensity of a vibration wave passed through a mass of concretewith respect of change in the distance from the source of the vibration;

f. Vibratability factor: A coefficient expressing the relationshipbetween a change in the intensity of vibration operating on a concretemass and the change in its resistance to shear deformation in a zoneaffected by the vibration;

g. Pumpability factor I: A coefficient expressing the relationshipbetween the pumping pressure and the rate of flow of a concrete masspumped through a pipe;

h. Pumpability factor II: A coefficient expressing the loss of pressurein a concrete mass along its passage through a given route in a pipingsystem;

i. Deformability factor: A coefficient expressing the relationshipbetween the force required to deform a confined mass of concrete and aresulting dimensional change occurring in one of its cross-sections.

It will be appreciated that not all of the characteristics providedhereinabove are required for all mixes. Different combinations of thecharacteristics, one of which normally is workability, can be utilized,as desired. The parameters forming the rheological profile that arerequired in a specific situation are determined by the nature of theconditions to which the concrete is to be exposed in the specificapplication. Furthermore, some of the parameters, such as pumpability,are not measured from the apparatus of FIG. 2 but from the otherapparati described hereinbelow.

The data is collected and processed, as will be described hereinbelow.The information can be used, for example, to advise the concretebatching plant of the actual rheology and quality of the concrete. Fromthis information, the mix design changer 6 (FIG. 1) can adjust theconcrete mix design to compensate for a change in the constituentcharacteristics or a change in actual site conditions and thus, allowthe plant to produce a more efficient and cost effective mix design.

Creation of Rheological Profile

Reference is now made to FIG. 5 which is a flow chart illustration ofthe design of a nominal rheological profile. A concrete mix based on astandard mix design having known proportions, for example, a 1:2:4 mixhaving a water/cement ratio of 0.45 is first produced (step 58). A"1:2:4" mix refers to the mix proportions, that is, one part of cementto 2 parts of fine aggregate to 4 parts of coarse aggregate.

A sample of the produced concrete mix is tested (step 60) to determineits properties and to compare it against the desired properties.

A sample of the concrete mix is then placed in a test mold (step 62), towhich the concrete testing device 10 is attached. The concrete mix isthen subjected to the first of a set of regimes (step 63), which areapplicable to the type of concrete mix being tested (step 64), forexample constant rate of deformation. The readings from the plurality ofsensors are recorded as the concrete undergoes change due to the forcesacting on it (step 66). Steps 63 to 66 are repeated for other regimes,such as different rates of deformation with or without vibration. Oncompletion of the applicable tests, the data is processed (step 68). Theresulting output defines the nominal rheological profile 70 for thespecific mix.

The resultant profile data, together with the mix design proportions anda description of the applications and materials domain under which themix was produced can be stored in a database for future access.

Due to the variability of the characteristics of the constituentmaterials, a mix design with given mix proportions could yield arheological profile different from the nominal rheological profile thatoriginally corresponded to the mix design, even if the workabilityvalues are equal. To achieve a profile which complies with the nominalrheological profile, the present invention adjusts the mix proportions,primarily of the solid elements of the mix, and typically, thereafter,the water and cement contents as well, as will be described hereinbelow.The adjustment is made to control the values of at least twoquantitative, measurable parameters of the profile, only one of whichdefines the resistance to deformation of the concrete mass, namely, itsworkability. In contrast, prior art methods use trial and errorprocedures to adjust proportions of water or water and cement so as toproduce a mix design with a desired, measurable workability value whilstchanges in aggregate constituents aimed to achieve desiredcharacteristics are conducted in a manner based on a concretetechnician's subjective assessment.

Overall Method of Controlled Concrete Production

Reference is now made to FIG. 6 which is a flow chart illustrating theuse of a nominal rheological profile to adjust the concrete mixproportions. A concrete mix is prepared (step 76) in accordance with aspecified design relevant to the type of concrete mix being required.The mix is measured, for example during mixing or pumping, using aselected concrete testing device 10 (step 78) for the specified regime.The recorded measurements are then converted to a rheological profilewhich reflects the measured mix (step 80). The measured rheologicalprofile is then compared with the designed nominal rheological profile(step 82). If the profile is within pre-determined limits, the design issatisfactory (83). If the rheological profile does not comply with thenominal rheological profile (within pre-determined limits), the mixproportions are amended (step 84) in accordance with pre-determinedcriteria and the revised mix is re-measured (step 78) and steps 80 and82 are repeated. If the revised mix does not produce the expectedrheological profile, steps 84 and 78-82 are repeated until the nominaland measured profiles match.

It will be appreciated that the adjustments to the mix composition canalso relate to powdery chemicals which regulate rheological behavior.

For each concrete mix composition there is a matching rheologicalprofile.

Mathematical Description of Mix Adjustment

The concrete mix design can be expressed by a variable p which is avector of mix proportions, where:

    p=(p.sub.1, p.sub.2, . . . , p.sub.k);                     (3)

    p.sub.1 +p.sub.2 + . . . +p.sub.k =1;                      (4)

k=number of mix components; and

p_(i) is the fraction of component i in the concrete mix. In otherwords, component i constitutes 100 p_(i) percent of the mix.

For example, a concrete mix having k=3 components comprising fines(30%), water and cement slurry (42%) and a third component representingall other concrete constituents (28%), may be expressed by:

    p=(0.3, 0.42, 0.28)                                        (5)

The rheological profile is composed of a number (n) of quantitativeindices that represent rheological characteristics of the concrete mix,such as workability, stress distribution at a point subjected to anaxial load or stress state sensitivity of the shear resistance. Thegeneral value of a rheological profile ρ may be denoted by the followingvector:

    92 =(ρ.sub.1, ρ.sub.2, . . . ρ.sub.n),         (6)

where each coordinate ρ_(i) represents a different rheologicalcharacteristic of the mix.

The target or nominal values of a rheological profile ρ* is denoted by:

    ρ*=(ρ.sub.1 *, ρ.sub.2 *, . . . ρ.sub.n *). (7)

The aim is to find a value for the independent variable p (mixproportions) which will yield a value ρ for the dependent rheologicalprofile variable which is "adequately close", that is, withinpre-determined limits, of the nominal value ρ*. The phrase "adequatelyclose" differentiates between constrained rheological characteristicsρ_(i) that satisfy the condition of:

    ρ.sub.1 ≦ρ.sub.1 *, ρ.sub.2 ≦ρ.sub.2 *, , ρ.sub.b ≦ρ.sub.b *; and                    (8)

target characteristics that must be fitted as close as possible to theircorresponding nominal values:

    ρ.sub.b+1 ≈ρ*.sub.b+1, ρ.sub.b+2 ≈ρ*.sub.b+2, , ρ.sub.n ≈ρ*.sub.n ; (9)

The phrase "adequately close" can be typically defined as:

    A.sub.b+1 (ρ.sub.b+1 -ρ*.sub.b+1).sup.2 + . . . +A.sub.n (ρ.sub.n -ρ*.sub.n).sup.2 ≦D;              (10)

where: A_(b+1), . . . , A_(n) are positive numbers modeling the severityof errors and D is a positive number modeling the tolerance allowed inthe global departure from the nominal values.

It is assumed that the rheological profile is a function of the concretemix proportions as long as the same materials are used. If theconstituent materials change, so does this function. This is the mainreason for the need to re-calibrate the mix proportions so as to achievethe nominal value of the rheological profile of the original mix.

The Search Process

To determine the mix proportions required for a mix having a givenrheological profile, several concrete mixes, each having different mixproportions, are produced. The specific rheological characteristics andhence, the rheological profile of each mix, are calculated. Since eachconcrete mix has different proportions, each of the rheologicalcharacteristics may have different values. Using standard mathematicaltools, such as the method of least squares, splines or interpolationpolynomials, applied iteratively, a "best-fit" curve, covering the rangeof values for each rheological characteristic, can be obtained.

The formula for the determination of the initial steps in the searchprocess could be mathematically calibrated using training data fromlaboratory experiments on the materials or based on arbitrary fieldpractice or general assessment.

With the assistance of suitable calculating tools, that are part ofcomputer software programs commercially available, such as the ExcelSpreadsheet produced by Microsoft Corporation of the USA, any mixcomposition can be simulated under the best-fit curve. A mix compositionyielding the desired nominal rheological profile under the best-fitmodel can be calculated and produced.

The rheological characteristics of the actual mix are compared with thecharacteristics of the design and if the rheological profiles do notmatch, the model is amended following the introduction of the new samplepoint. The mix proportions are amended accordingly (step 84 of FIG. 6).The incremental changes in the mix proportions are mathematicallydesigned so as to achieve the desired new mix design.

Thus, it is possible to design a concrete mix which matches somerequired properties of the mix made with the original material. Thisallows for a better control over the production of concrete mixes. Steps80-84 are repeated until the rheological profile of the produced mixmatches the pre-determined criteria for that mix.

This mathematical simulation procedure can find a domain of feasibleapproximate solutions, (that is, the mix compositions are feasible withrespect to the interpolation function). The choice of mix is made takingaccount of economic considerations, that is, the cost optimizationfunction sets boundaries in the search procedure.

Standard analysis software packages, such as the EXCEL spread sheet byMicrosoft Corp. of the USA. or more advanced mathematical programs suchas the Mathematical from Wolfram Research Inc. of Champagne, Ill.,U.S.A. or MATLAB manufactured by The MathWorks Inc. of the USA, containtools for the minimization of linear or non linear objective functionssubject to a set of constraints, which can be incorporated within themathematical formula for the calculation of the economically efficientmix compositions. These mathematical techniques will be applied in thecontext of the invention not only to the objective defined above,namely, the search for a concrete mix composition that matchesadequately close a given target rheological profile, but also tosituations where such a nominal profile is fully or partially absent. Inthis case, the same interpolation and search procedure will be appliedto find a concrete mix composition that optimizes a given criterionfunction. For example, it may be applied to:

a. minimize the cost of the concrete mix whilst maintaining the pressureon the piston of a pump as required to push concrete at a given ratethrough a given pipe system;

b. minimize the cost of the concrete mix whilst maximizing the bulkdensity of a concrete block produced under a given regime,

c. minimize water/cement ratio of a block making mix maximizing thecompressive strength of a freshly made block (prior to hardening); or

d. minimize the cost of a concrete mix whilst maintaining force requiredto rotate the drum of a concrete mixer at a given rate under givenconditions.

Controlling Concrete Production Under Other Conditions

The alternative method is operative with a concrete processing device,such as a pump or a block making machine, as illustrated in the flowchart of FIG. 7, to which reference is made. Reference is also made toFIG. 8 which illustrates, in flow chart format, the alternative method.

The concrete processing device, labeled 900, receives already mixedconcrete from a batching plant 902 via a mixer 904. A sensing device906, which can have more than one sensor therein, monitors variousparameters of the operation of the processing device 900. For example,if the processing device 900 is a piston pump which forces concretethrough a pipe system, the sensing device 906 monitors the force orpressure on the pump, the extension of the piston and the rate at whichconcrete exits the pipe system. No measurements of the concrete itselfare taken.

The output of the sensing device 906 is provided to a mix design changer908 which, as indicated in step 910 of FIG. 8, analyzes the parametersand, in step 912, provides change commands to the batching plant 902 tochange the amount of fine sand (or other solid components of the mix).The process is repeated a number of times.

In step 914, the mix design changer 908 reviews the design mix at eachpoint and its resultant parameter and selects the design mix whichprovides a desired set of parameter values within a given constraint.For example, it might select the lowest cost mix design which providesconcrete that flows in the given pump at a rate of 2 meter/sec andutilizes the maximum amount of force at which the pump can operate.

Alternative Embodiments of the Concrete Tester

Reference is now made to FIGS. 9A and 9B which illustrate a secondembodiment of the concrete testing device, generally designated 108. Thetesting device 108 comprises a shear box 110 and a propeller 118. Shearbox 110 comprises two side panels 112a and 112b connected to a basepanel 114 and has open sides 116. An aperture 117 is formed within basepanel 114 for the insertion of propeller 118.

Propeller 118 comprises an electrical motor 120 enclosed within ahousing 122. A vertical drive shaft 124, suitably retained by housing122, is attached to propeller blades 126. Drive shaft 124 and propellerblades 126 extend below shear box 110 and are retained in position byany suitable means which allows drive shaft 124 to freely rotate.Housing 122 and motor 120 are enclosed within a chamber 127 to protectthem from the concrete. A tachometer 128 is connected to shaft 124 tomeasure the speed of rotation of propeller 118. An ammeter 130, orsimilar electrical measuring device, is fitted to the upper part ofhousing 120 to measure the power used by propeller 118. Furthermore,changes in current occurring within each cycle in the propeller rotationare also recorded.

A multiplicity of stress sensors 132 are fitted to the underside of sidepanels 112a and 112b and base panel 114 of shear box 110. As describedhereinabove with respect to the embodiment of FIG. 2, the sensors are intwo planes so that the stress state in the concrete can be monitored.

In operation, shear box 110 is inserted into the concrete mass, andpropeller mixer 118 is switched on. Propeller blades 126 rotate, forcingthe concrete forward (indicated by arrows 134 in FIG. 9B) and causingthe concrete to shear. When the propeller blades rotates, they are belowthe side planes 112a and 112b half of the time and away from them theother half of the time. Thus, the shape of the space within which theconcrete is held changes cyclically. For various speeds of propeller118, the current, mixer speed and sensor data are collected and passedon to the processing unit (not shown), as hereinabove described.

FIG. 9C, to which reference is now briefly made, illustrates exemplaryresistance vs. shear deformation results for the two mixes of FIG. 4Cwithin the embodiment of FIGS. 9A and 9B. Since the shape of the spacewithin which the concrete is held changes cyclically, the curves of FIG.5C, labeled 140 and 142, change periodically. The resistance datapointsof interest are those at the extreme ends of one cycle of change. Thus,the two datapoints R₁ ⁰ and R₂ ⁰ of the first mix are spread furtherapart than are the two datapoints R₁ ¹ and R₂ ¹ of the second mix.

Reference is now made to FIGS. 10A and 10B which illustrate a device fortesting concrete within a pumping system, generally designated 300,constructed and operative in accordance with a fourth and fifthembodiment of the invention. This embodiment measures at least thepumpability factors I and II and the shear rate sensitivity factor, asdescribed hereinabove.

Generally, concrete pumping system 300 comprises a pump 310 and a hopperattachment 312 coupled to a system of pipes 314. A multiplicity ofpressure sensors 316 are attached to the inside of pipes 314. Sensors316 sense the changing pressure and stress levels as the concrete ispumped through the pipes 314. Additionally various sensing devices,described in detail hereinbelow, are connected to pump 310 to measureoperational parameters of the pump.

In operation, concrete is discharged into hopper 312 and forced alongthe system of pipes 314 by the action of the pump 310, where the pumpcyclically changes the shape of the space through which the concrete ispumped. As hereinabove described with respect to FIG. 2, the data iscollected and passed onto the processing unit 100 for processing. Means,as known in the act, are provided to prevent backflow from pipe 314 intothe pump.

In the concrete pumping system illustrated in FIG. 10A, an electric pump320 is attached to a screw device 322 which propels the concrete alongpipes 314. The sensing devices also comprises an ammeter 324, or othersimilar measuring device, which is fitted to pump 310 to measure thecurrent used by electric pump 310 whilst changes in current occurringwithin each cycle of the screw rotation or position movement are alsorecorded. A tachometer 326, or other similar device for measuring thespeed of rotation of screw device 322, is fitted to pump 320. It isnoted that, as the screw 322 rotates, the distance between the upperpart of the screw, labeled 321, and the pipe entrance, labeled 323,changes cyclically.

In the concrete pumping system 300 illustrated in FIG. 10B, a hydraulicpump 330 is attached to a piston device 332, such as a single piston ordouble piston action, as is known in the art. The action of the pistonpropels the concrete along pipes 314, slowly changing the shape of thespace through which the concrete is pumped. In this embodiment, thesensing devices comprise a manometer 336, or similar device, formeasuring the hydraulic pressure of the hydraulic pump 330. In addition,the system of FIG. 10B has an electronic ruler 313 to measure thedisplacement of the pump. This embodiment can also include a vibrator311 to provide a measurement of vibratability.

Reference is now briefly made to FIG. 11 which illustrates the use ofspecially adapted pipe inserts within the pumping system 300, fortesting the concrete. Similar elements in FIG. 11 serve similarfunctions and are referenced by similar reference numerals.

In FIG. 11, an adapted pipe 410, having a generally smaller diameterthan the standard pipes 314 of pumping system 300, described above, iscoupled to the pipes 314. A multiplicity of pressure sensors 412 areattached to the inside of adapted pipe 410. The changing stress state ofthe concrete due to the change in shape of the pipe can be monitoredfrom the data supplied through the multiplicity of sensors 412 fittedwithin adapted pipe 410 and standard pipes 314, both upstream anddownstream of adapted pipe 410.

Reference is now briefly made to FIGS. 12 and 13. FIG. 12 illustrates anisometric view of a sixth embodiment of the concrete testing device,generally designated 510. FIG. 13 shows a sectional detail of concretetesting device 510 which is specially adapted to be inserted into a 90degree pipe bend 512 of a pumping system.

A 90 degree bend 512 is generally used, for example, in a pumping systemwhere the concrete is pumped upwards out of hopper 516 (as illustrated).The device 510 measures the changing stress state and loss of pressurecaused by sharp bends.

Testing device 510 comprises a locking cover plate 514, which replaces acover plate, commonly fitted at the exit (or entrance) of a pipe system.Flexible strips 518 extend perpendicularly from the inside face of coverplate 514. Sensors 520 and 522 are fitted to flexible strips 518.

Reference is now made to FIGS. 14A and 14B which illustrate the use of aconcrete testing device with a paddle mixer, generally designated 600.Concrete testing device can be any concrete testing devices, constructedin accordance with the preferred embodiment of the present invention.FIG. 14A illustrates a concrete testing device 200, describedhereinabove with respect to FIG. 10, which can be inserted into paddlemixer 600 from above when the paddle mixer is stationary. FIG. 14Billustrates a concrete testing device, generally designated 620, locatedbelow paddle mixer 600.

Generally, concrete paddle mixer 600 is a standard paddle mixer, knownin the art, which comprises a mixing pan 602, and a plurality of paddles604 attached to a revolving shaft 606. To mix the concrete, shaft 606cause paddles 604 to revolve. The mixing action forces the concrete outof the bottom of pan 602. Data is collected by concrete testing device200 and passed on to the processing unit (not shown), as previouslydescribed.

Referring now to FIG. 14B, concrete testing device 620, comprises ahydraulic pump 622 attached to a piston device 624, such as a singlepiston or double piston action, as is known in the art. Piston device624 is enclosed within a housing 626, located beneath pan 602, having aninlet gate 628 and an outlet 630 constructed therein. An opening 632 isconstructed in the base of pan 602 to accommodate inlet gate 628. Amultiplicity of sensors 634 are attached to piston device 624, such asto measure the pumping pressure, displacement of the piston and thestress state along the pipe. Optionally, a vibrator 636 can be fitted tothe base of piston device 624.

When inlet gate 628 is opened and concrete enters housing 626, theaction of piston device 624 pushes the concrete through opening 632.Measurements can be made with or without vibration as desired. Data iscollected by the multiplicity of sensors 634 and passed on to theprocessing unit (not shown), as previously described.

Reference is now made to FIG. 15, which illustrates a concrete testingdevice 700 adapted for use with a mobile mixer 710. Concrete testingdevice 700 comprises a rod 702 having a plurality of sensors 704attached to one end thereof. In one mode of this embodiment, thedeformation is provided by the rotating drum 706. Alternatively, the rodcan include a mechanical deforming unit with monitoring sensors, such asshown in FIG. 9. Rod 702 is inserted within the drum 706 of mixer 710.Data collected by sensors 704 are passed on to the processing unit 100,as previously described. Optionally, a multiplicity of sensors 708 canbe attached to a shear box mounted on the inside of drum 706. In such adevice, the output of the sensors is provided to a processing unit 712located on the rotating drum which transmits the data, typically in awireless fashion, to remotely contact processing unit 100, which may,for example, be situated at the mixing plant.

Reference is now made to FIG. 16, which illustrates the productioncontrol of concrete blocks 800, of a type commonly manufactured for usein the construction industry, wherein concrete is cast in a mould 802defining the shape of the concrete block 800. A factory production line804 is shown on which a plurality of cast concrete blocks 800 areplaced. In order to control the production quality and cost, one of theplurality of concrete blocks 800, designated 810, is removed from theproduction line 804 for testing. The weight and the size of the concreteblock 810 can be measured using electronic measuring devices 806 and808, respectively, known in the art. A compression testing frame 809measures the fresh compressive strength of the block 810. If desired,the rheological profile of the mix used for creating the blocks can bedetermined using a selected concrete profile measuring device 10, ashereinbefore described. In this case, the rheological profile of thefresh mix is gained with the measurements of the block and compared withthe nominal rheological profile for this type of block, and if it doesnot match, the mix proportions can be adjusted as hereinbefore describedwith respect to FIG. 6. Alternatively, only the block measurements canbe produced and an optimization such as described in FIGS. 7 and 8 canbe preformed.

As will be appreciated by persons knowledgeable in the art, the variousembodiments hereinabove referred are given by way of example only and donot in any way limit the present invention. For example, apart from theillustrated changes of fines, water and cement, the addition of chemicaladditives can be controlled to provide a desired rheology.

Those skilled in the art will be readily appreciate that variouschanges, modifications and variations may be applied to the preferredembodiments without departing from the scope of the invention as definedin and by the appended claims.

I claim:
 1. A measuring system for measuring rheological properties of aconcrete mix tested when contained, the system comprising:a surface incontact with a part of a mass of said concrete mix; a shearing unit foreffecting shear deformation in said mass; at least one sensor whichsenses a measure of the force which is transferred to said surface bysaid concrete mass as a result of said shear deformation under at leasttwo measurement environments defining at least two different stressstates; and a confining envelope, wherein a space defined between saidconfining envelope and a rigid body of said shearing unit significantlychanges shape with the movement of said rigid body during sheardeformation, and wherein said at least one sensor senses a measure ofthe resistance of said concrete mass to shear during the operation ofsaid shearing unit, wherein said resistance significantly changes duringsaid operation as a result of said change in shape.
 2. A method forgenerating a rheological profile of a given concrete mix, the methodcomprising the steps of;effecting shear deformation in a mass of saidconcrete mix; sensing at least two measures relating to the resistanceof said concrete mass to said shear deformation; generating, from saidat least two measures, at least one variable relating to the workabilityof said concrete mix; generating at least one additional variable fromthe ratio of two of said at least two measures; and creating saidrheological profile from said variables, wherein said concrete masschanges shape during said step of effecting shear deformation, andwherein said step of sensing senses at least two different measures ofthe resistance of said concrete mass to shear during said sheardeformation.
 3. A method for the control of production and the design ofconcrete mixes to have desired rheological properties, the methodcomprising the steps of:preparing a concrete mix in a concrete plant inaccordance with a mix design indicating the proportions of solidcomponents and water content of the concrete; testing said preparedconcrete mix with a concrete tester; generating a rheological profile ofsaid concrete mix from output of said step of testing; comparing saidgenerated rheological profile with a desired rheological profiledefining desired properties of the concrete to be produced by saidplant; and adjusting said proportions of said solid components of saidmix design in order to produce concrete having a rheological profilewhich is compatible with said desired rheological profile, wherein saiddesired rheological profile comprise a measure of workability and atleast one of the following factors and their related functions: stressstate sensitivity, stress distribution, shear rate sensitivity,vibration decay, vibratability, pumpability and deformability.
 4. Asystem which designs and produces concrete to have desired rheologicalproperties, the system comprising:a plant for preparing a concrete mixin accordance with a mix design indicating the proportions of the solidcomponents and water of the concrete; a concrete profile measuring unitfor measuring a rheological profile of the concrete produced by saidplant; and a mix changing unit for receiving said measured rheologicalprofile and a desired rheological profile defining desired properties ofthe concrete produced by said plant and for indicating to said plant toadjust said solid components of said concrete mix, as many times asnecessary, in order to produce concrete which has a rheological profilewhich is compatible with said rheological profile, said mix changingunit comprising a search unit for receiving a quality of changecriterion and for determining the mix design change which will provideconcrete having said rheological profile which is compatible with saiddesired rheological profile and which fits within said quality of changecriterion, wherein said criterion is a function of the cost of the mix.